Supercharger

ABSTRACT

A centrifugal supercharger is provided. One embodiment of the supercharger comprises a two-piece housing wherein a parting area is substantially aligned with a rotational axis of a drive or impeller shaft. Another embodiment comprises a sleeve, or intermediate member disposed substantially between the housing and a bearing assembly(s) located within the supercharger housing. Another embodiment comprises a disengagement device located between the supercharger impeller and the engine. The disengagement device allows selective disengagement of the impeller from the engine. This Abstract is provided for the sole purpose of complying with the Abstract requirement rules that allow a reader to quickly ascertain the subject matter of the disclosure contained therein. This Abstract is submitted with the explicit understanding that it will not be used to interpret or to limit the scope or the meaning of the claims.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of co-pending U.S. application Ser.No. 11/470,114 filed Sep. 5, 2006 entitled “Supercharger,” which is acontinuation of U.S. application Ser. No. 10/698,192 filed Oct. 31,2003, entitled “Supercharger,” now U.S. Pat. No. 7,128,061, issued Oct.31, 2006.

FIELD OF THE INVENTION

The present invention generally relates to superchargers. Moreparticularly, the invention concerns a centrifugal supercharger.

BACKGROUND OF THE INVENTION

Superchargers have become pervasive in automobiles, boats, aircraft, andcommercial stationary engines as the need to maximize power output hasincreased due to the use of smaller engines. Centrifugal superchargersemploy a high-speed impeller to develop their boost pressure. Althoughsuch high-speed machinery places extreme demands on the associated drivemachinery, e.g., bearings, seals, shafts, housing components, and thelike, centrifugal compressors benefit from very high thermodynamicefficiencies, resulting in optimum engine outputs.

Most centrifugal superchargers employ some sort of speed increasingmechanism to provide the rotation speed for the centrifugal compressorportion of the device to work. This mechanism, which is usuallycomprised of two parallel shafts with either a belt or gear systemconnecting them, requires matching cylindrical bores for the shafts andbearings. In the current art, a minimum of two bearing bores and twolocating pin bores are machined in each part that comprise thesupercharger case and cover, and the two are assembled like two halvesof a clam shell, e.g. the separating plane of the individual casecomponents is orthogonal to both shafts. This process requires eight (8)precision boring operations. A significant problem exists inmanufacturing the very precise bores of the case components. Forexample, the accuracy needed to obtain the desired relationship betweenthe two shafts requires true position and parallelism tolerances of0.0005 inches. These extremely tight tolerances challenge thecapabilities of even the newest and best state-of-the-artcomputer-controlled machining centers. Manufacturing these assembliesrequires expensive and time-consuming set-up, machining, measuring andmatching procedures. Even with very careful manufacturing procedures, asignificant component rejection rate exists, due to parts that do notmeet the strict tolerance requirements.

In view of the above, there exists a need for an efficient superchargerthat is easy to manufacture and service.

SUMMARY OF THE INVENTION

The present invention provides a very efficient supercharger that iseasy to manufacture and service.

One feature of the present invention comprises a supercharger that has acase, or housing that is split into a primary section and a removablesection. This two-piece housing greatly enhances and simplifies theability to attain the required precision manufacturing tolerances.

Another feature of the present invention comprises a sleeve, orintermediate member disposed substantially around a shaft located withinthe supercharger housing. The intermediate member may be used on thedriveshaft, the impeller shaft, or may be used on both shafts. Betweenthe intermediate member and the shaft are bearing assemblies that allowthe shafts to rotate. One feature of the intermediate member is that ithas a coefficient of thermal expansion (CTE) that is substantiallysimilar to the CTE of the bearing assemblies.

Yet another feature of the present invention comprises a disengagementdevice located between the supercharger impeller and the engine, ormotor that drives the supercharger. The disengagement device allowsselective disengagement of the impeller from the engine.

A further feature of the present invention comprises an impeller shaftsupport designed to reduce mechanical stress and associated rotodynamicinstabilities.

Yet another feature of the present invention comprises a superchargerimpeller having at least three sets of blades. A first set of primaryblades has a first height and a set of secondary, or splitter bladeshave a second, shorter height. A third set of splitter blades has athird height that is less than the height of the second set of splitterblades.

Another feature of the present invention comprises a supercharger havinga modular compressor housing. The modular compressor housing includestwo or more modular components. In one embodiment, the compressorhousing includes a main housing and a shroud. In other embodiments, thecompressor housing includes a main housing, a shroud and a diffuser.

These and other features and advantages of the present invention will beappreciated from review of the following detailed description of theinvention, along with the accompanying figures in which like referencenumerals refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing a supercharger, its driveshaft, and pulleyarrangement attached to an engine;

FIGS. 2A and 2B are cross-sectional and exploded views, respectively, ofa supercharger in accordance with the principles of the presentinvention;

FIG. 2C and 2D are plan, and elevation views, respectively, of an oilreservoir cover for use with the supercharger of the present invention;

FIGS. 3A and 3B are cross-sectional views of a sleeve assembly for usewith the supercharger of the present invention;

FIG. 3C is an isometric view of an impeller shaft cartridge assembly foruse with the supercharger of the present invention;

FIG. 3D is cross-sectional view of a portion of the supercharger of thepresent invention, illustrating a lubrication conduit and an end view ofthe impeller shaft and sleeve;

FIGS. 4A and 4B are exploded and cross-sectional views, respectively,depicting a disengagement device for use with the supercharger of thepresent invention;

FIG. 4C illustrates a graph of an impeller shaftacceleration/deceleration rate of a conventional supercharger;

FIG. 4D illustrates a graph of an impeller shaftacceleration/deceleration rate of a supercharger constructed accordingto one embodiment of the present invention;

FIGS. 5A and 5B are cross-sectional views of a spacer assembly for usewith the supercharger of the present invention;

FIGS. 6A and 6B are perspective and side views, respectively, of animpeller for use with the supercharger of the present invention; and

FIGS. 7A and 7B are side and exploded views, respectively, of a modularcompressor housing for use with the supercharger of the presentinvention.

It will be recognized that some or all of the Figures are schematicrepresentations for purposes of illustration and do not necessarilydepict the actual relative sizes or locations of the elements shown. TheFigures are provided for the purpose of illustrating one or moreembodiments of the invention with the explicit understanding that theywill not be used to limit the scope or the meaning of the claims.

DETAILED DESCRIPTION OF THE INVENTION

In the following paragraphs, the present invention will be described indetail by way of example with reference to the attached drawings.Throughout this description, the preferred embodiment and examples shownshould be considered as exemplars, rather than as limitations on thepresent invention. As used herein, the “present invention” refers to anyone of the embodiments of the invention described herein, and anyequivalents. Furthermore, reference to various feature(s) of the“present invention” throughout this document does not mean that allclaimed embodiments or methods must include the referenced feature(s).

Referring to FIG. 1, a supercharger 10 constructed according to thepresent invention includes a driveshaft 12 for receiving rotationalforce from an engine 14 via a pulley and belt assembly 16. Moreparticularly, one end of the driveshaft 12 is attached to supercharger10 and the opposite end is attached to the pulley and belt assembly 16.In the illustrated embodiment, driveshaft 12 is depicted as relativelylong with respect to the other engine components. However, driveshaft 12may be considerably shorter such that the supercharger is in closeproximity to the pulley and belt assembly 16 without departing from thescope of the present invention. Furthermore, driveshaft 12 may bycomprised of an additional shaft member with supporting bearingstructure such as described in U.S. Pat. No. 6,092,511 without departingfrom the scope of the present invention.

Referring to FIGS. 2A and 2B, supercharger 10 comprises driveshaft 12,impeller shaft 20, impeller 22, compressor housing 24, gear housing 26and lubrication reservoir 28. In operation, air is drawn through opening24 a in the compressor housing 24 and into impeller 22. Impeller 22, inconjunction with the compressor housing 24, compresses the air beforedischarging it out of the compressor housing 24. Preferably, impeller 22is designed to discharge the air smoothly into compressor housing 26,without substantial discontinuity or aerodynamic perturbation that mayreduce performance.

Driveshaft 12 is mechanically coupled to impeller shaft 20 such thatrotation of the driveshaft imparts rotation on the impeller shaft 20,thereby causing rotation of impeller 22. The mechanical coupling betweenthe input drive and impeller shafts includes a drive gear 30 disposedabout driveshaft 12 and an impeller gear (not shown) disposed aboutimpeller shaft 20. In a preferred embodiment, the drive gear 30 has alarger circumference than the impeller gear, thereby causing theimpeller gear to rotate faster than the drive gear 30.

As shown in FIGS. 2A and 2B, the gear housing 26 defines a chamber thatcontains the drive gear and impeller gear. Gear housing 26 includes aprimary section 26 a and a removable section 26 b configured to matewith the lower section. Removable section 26 b is attached to primarysection 26 a by way of conventional removable fasteners 34 such asscrews or bolts, which pass through apertures 34 a in the removablesection and corresponding apertures 34 b in primary section. Gearhousing 26 also contains driveshaft bearing assemblies 38 a, 38 bdisposed on either side of drive gear 30 and impeller shaft bearingassemblies 40 a, 40 b disposed on either side of the impeller gear (notshown). Bearing assemblies 40 a, 40 b may comprise single or multiplebearing elements. The bearing elements may be deep-groove or angularcontact types, without departing from the scope of this invention.Advantageously, and in the case of multiple angular contact bearingelements, the bearing assemblies 40 a, 40 b may be configured in tandempairs (shown), or may be rigidly preloaded duplex sets, configured ineither “DF” or “DB” arrangements.

The impeller gear (not shown) is coupled to impeller shaft 20 such thatthe rotation of impeller gear imparts rotation to the impeller shaft andimpeller 22. Drive gear 30 is connected to driveshaft 12 such that therotation of drive gear 30 imparts rotation to the impeller shaft 20.

As best seen in FIG. 2B, removable gear housing section 26 b includes asemicircular recess 31, which, in combination with a correspondingrecess 33 in primary gear housing section 26 a, provides an openingdimensioned for the passage of driveshaft 12. Gear housing 26 is therebysplit in two sections along a dividing plane that is substantiallyparallel with the rotational axis of driveshaft 12. In the illustratedembodiment, the dividing plane is substantially coplanar with therotational axis of the driveshaft 12. Removing the removable gearhousing section 26 b provides access to driveshaft 12, drive gear 30 anddriveshaft bearing assemblies 38 a, 38 b. It will be appreciated thatthe gear housing 26 may be split in any number of different ways. Forexample, the gear housing 26 maybe split along a dividing plane that issubstantially parallel with the impeller shaft 20. Alternatively, thegear housing 26 may be split along multiple dividing planes that may besubstantially parallel with both the impeller shaft 20 and thedriveshaft 12. Or, the gear housing 26 may be split along other suitableplanes.

One feature of this aspect of the invention is that the demandingmanufacturing tolerances for the gear housing 26 are much easier toachieve, thereby increasing manufacturability, and decreasing wastegenerated by parts that are out-of-tolerance. In addition, the number ofprecision machining operations required to manufacture the gear housing26 can be significantly reduced, e.g., from 8 individual boringoperations to two. Advantageously, this reduces manufacturing costs. Inaddition, this invention feature adds rigidity to the supercharger 10,and maximizes the manufacturing precision, thereby resulting in improvedalignments between gears and shafts for smoother, quieter operation,simplified manufacturing processes, and reduced overall manufacturingcosts.

Again referring to FIGS. 2A, 2B and 4A, gear housing 26 preferablyincludes a cover plate 42, that when removed provides access to theimpeller shaft 20, impeller gear (not shown) and impeller shaft bearingassemblies 40 a, 40 b. The cover plate 42 includes an aperture 44dimensioned for the passage of the driveshaft. The cover plate 42 isremovably attached to the gear housing primary section 26 a by way ofcover plate fasteners 46 such as screws, bolts or equivalents, whichpass through cover plate apertures 48, and into corresponding gearhousing apertures 50 in the gear housing primary section 26 a. Inaddition, the cover plate 42 is attached to the gear housing removablesection 26 b by way of conventional fasteners 46 such as screws, boltsor equivalents, which pass through cover plate apertures 48, and intocorresponding gear housing apertures 52 in the gear housing removablesection 26 b.

Some centrifugal superchargers employ the existing lubrication system ofthe host engine for the supercharger lubrication. However, there existseveral advantages of having a self-contained supercharger lubricationsystem, wherein the supercharger's lubricating fluid is separate fromthe engine's lubricating fluid. One advantage of a self-containedlubrication system is simplification and ease of installation. Someexisting supercharger self-contained lubrication systems utilize asplash system wherein one or more gears are dipped into an oil bath.However, these designs suffer from the disadvantage that built-up heatcannot be discharged.

Referring again to FIG. 2A, according to another embodiment of thepresent invention, lubrication reservoir 28 is self-contained within thegear housing 26 such that the supercharger 10 does not requirelubrication to be drawn from an external source, such as the engine 14.Additionally, in another embodiment of the present invention, thelubrication reservoir 28 is preferably separate and detachable from thegear housing 26, thereby reducing service and repair costs. Lubricationreservoir 28 further includes at least one lubrication inlet 54 and atleast one lubrication outlet 56. The lubrication is preferably either inthe form of oil, such as engine oil, or in the form of an oil-air mistdelivered by appropriate means such as an atomizer (not shown).Advantageously, in a preferred embodiment, hot lubricating fluid isdrained into the lubrication reservoir 28 via the lubrication inlet 54and allowed to cool before being recirculated.

Some superchargers provide an air-assist approach to augmentinglubricating oil circulation within the supercharger gearcase. Generally,the air assist approach results in an air-oil mist lubrication, whichaids in achieving reliable operation and the minimization of bearingassembly failure.

In one embodiment of the present invention, the supercharger 10preferably includes an air assist approach, wherein compressed air fromthe supercharger 10 is introduced into the lubricating oil by use of amixing air-assist nozzle assembly (not shown). Such an air-assistassembly may be similar to one described in U.S. Pat. No. 6,293,263. Inoperation, engine oil, under pressure, mixes with supercharger dischargeair, also under pressure, and introduces an air-oil lubricating mistinto the supercharger. The lubricating mist is preferably directedtowards the supercharger 10 internal gear, shaft, and bearingcomponents.

One advantage of using an oil/air mist is that the oil can be readilysprayed onto the gears and bearings, thereby maximizing gear and bearinglife. Further, the pressurized air atomizes the oil and improvesdistribution and also assists in driving the oil out of the gear housing26 after use (and into the lubrication reservoir 28), thereby minimizingthe oil cycle time in the gear housing 26, and providing improvedlubrication and cooling of the gears and bearings.

Referring to FIGS. 2A, and 2C-D, some embodiments of the presentinvention may include a reservoir 28 having a reservoir baseplate 29that may include inlet and outlet ports 32 for the circulation ofcooling fluid or water. As shown in FIG. 2D, such an embodimentincorporates passageways communicating with the inlet and outlet ports32, but that do not communicate with reservoir 28. The passagewayssupply cooling fluid to the heat transfer elements 35, that are incontact with any lubricating oil within reservoir 28. The cooling fluidcan be provided from a variety of sources including the engine coolingsystem, or in the case of a marine application, lake or sea water.Advantageously, as shown in FIGS. 2C-D, the heat transfer elements 35,are attached-to or cast-into the baseplate 29 and provide improvedcooling performance.

Referring now to FIGS. 3A-D, the precision bearing fit and alignmentrequired for high-speed supercharger operation is often difficult tomaintain. One problem stems from the intrinsic difference in thecoefficient of thermal expansion (CTE) between the bearing assemblies,which are typically ferrous-based, and the gear housing, which isusually made of aluminum. For example, the CTE for aluminum isrelatively high (0.00001244 unit length change, per degree Fahrenheit)when compared to ferrous materials such as cast iron (0.00000655),carbon steel (0.00000533), and 440C stainless steel (0.0000056). Mostbearing assemblies, such as those used by the present invention, arecomprised of steel or ceramic (Silicon Nitride) rolling elements,retained in angular position and alignment by a cage, and interposedbetween inner and outer steel races. Typical material of the steel raceswould be SAE52100 ferrous-based steel, although other ferrous-basedmaterials may be used including 440C, and martensitic Chromium steelswith homogeneous carbonitride microstructure.

As shown in FIGS. 3A-D, according to another aspect of the presentinvention, an intermediate member, sheath, or sleeve 60 is disposedaround the impeller shaft bearing assemblies 40 a, 40 b. Sleeve 60preferably comprises a ferrous-based material having a CTE that issubstantially similar to the CTE of the bearing assemblies 40 a, 40 b.According to some embodiments, the CTE of the sleeve preferably includesa CTE that may range between about 0.000004 and about 0.000007 in/in-°F. (i.e., 4.0×10⁻⁶, and 7.0×10⁻⁶ in/in-° F.). Suitable ferrous-basedmaterials for the sleeve 60 include, but are not limited to, grade G2gray iron, DURA-BAR®, free-machining steels such as 12L14, and all otherferrous-based materials having a CTE that is substantially similar tothe CTE of the bearing assemblies 40 a, 40 b (DURA-BAR is a registeredtrademark of Wells Manuf. Co. of Skokie, Ill.).

As shown in FIGS. 3A-D, the sleeve 60 includes an opening 62 for gearengagement. Additionally, the sleeve 60 includes a lubrication conduit64 in fluid communication with a lubrication oil supply conduit 51, andlubrication apertures 65 in fluid communication with lubrication conduit64. Lubricating oil may then drain back to reservoir 28 via drain port66, which is aligned to be in communication with port 54 (shown in FIG.2A). It will be appreciated that the sleeve, or sheath 60 may compriseany configuration that results in the sleeve, or intermediate memberbeing positioned between the bearing assemblies 40 a, 40 b and the gearhousing 26. The intermediate-member may also be comprised of more thanone component.

According to some embodiments, the intermediate member, or sleeve 60 ispressed or shrink-fitted into the gear housing 26. In other embodiments,sleeve 60 may be installed with a clearance fit into housing 26, andretained thereto by a fastener, or other suitable device.

Referring now to FIG. 3D, in the illustrated embodiment, a replaceableshaft-bearing cartridge 68 comprises sleeve 60, bearing assemblies 40 a,40 b, and impeller shaft 20. The shaft-bearing cartridge 68 installsinto supercharger primary section 26 a with a slight clearance fit,resulting in an annular gap 67, interposed between sleeve 60 and primarysection 26 a. In one embodiment, the annular gap 67 may range from about0.0015 inch to about 0.0002 inch. This gap may change with any change intemperature of the sleeve 60 or the primary section 26 a.

In a preferred embodiment, lubricating oil, supplied under pressure viaconduit 51, which is in communication with conduit 63, is forced intoannular gap 67 and creates a hydrostatic supporting force, which reactsto gear loads during supercharger 10 operation. Advantageously, thishydrostatic load supporting mechanism also promotes vibration dampingcharacteristics, resulting in quieter operation of the supercharger 10.

One feature of the sleeve 60 is that it maintains the bearing assemblies40 a, 40 b securely in the gear housing 26 during a range ofsupercharger 10 operating temperatures. More importantly, the fitbetween bearing races 40 a, 40 b and sleeve 60 are maintained regardlessof operating temperature. This is achievable because the CTE's of thesleeve 60 and the bearing assemblies 40 a, 40 b are substantiallymatched, thereby expanding and contracting in unison. This feature isespecially beneficial to the high-speed impeller shaft 20 bearings 40 a,40 b, which may operate at speeds exceeding 60,000 RPM. It will beappreciated that a sleeve(s) 60 may also be placed around the driveshaftbearing assemblies 38 a, 38 b.

Referring now to FIG. 3C, the shaft-bearing cartridge 68 may be employedas an insertable device that lends itself to manufacturing and assemblyadvantages in addition to the aforementioned thermal stabilityadvantage. For example, the shaft-bearing cartridge 68 permitspre-assembly which allows it to be inserted and/or removed as a singleunit, thereby reducing service and repair costs. Additionally, the useof a pre-assembled, replaceable shaft-bearing cartridge 68 allowsrepairs to be performed in the field.

Referring to FIGS. 4C-D, superchargers can experience very fast drive-and impeller shaft acceleration rates. The acceleration rates areamplified by the step-up ratio between the driveshaft 12 and theimpeller shaft 20, which is typically in the range of 3:1 to 5:1 (i.e.,3 to 1 and 5 to 1). That is, the impeller shaft 20 may rotate five timesfaster than the driveshaft 12. High acceleration and decelerationforces, generally caused by “blipping” the engine, can stress theimpeller shaft 20 and its related components, and cause de-stabilizingeffects of bearings 40 a, 40 b, sufficient to cause catastrophicfailure. However, the most severe stresses and bearing instabilitiesgenerally occur during the transition from very high to relatively slowimpeller shaft 20 rotational speeds. An extreme example would be a veryrapid rotational acceleration immediately followed by a very rapiddeceleration. Such an acceleration rate with the peak point ofdestabilization is depicted in FIG. 4C.

Again referring to FIGS. 4A and 4B, according to another feature of thepresent invention, the supercharger 10 preferably includes adisengagement device 70 for disengaging the impeller 22 from the engine14. In the illustrated embodiment, the driveshaft 12 is disengageablefrom the engine 14. As best seen in FIG. 4B, the disengagement device 70is disposed between the driveshaft 12 and the primary drive pulley 72.According to some embodiments, the disengagement device 70 comprises aone-way clutch, such as a sprag, overrunning clutch, or other suitabledevice. In a preferred embodiment, the disengagement device 70 ispreferably integrated into the primary drive pulley 72, which may alsocomprise part of belt and pulley system 16, as described in FIG. 1.

As shown in FIG. 4B, in a preferred embodiment, the disengagement device70 comprises a sprag clutch 71 located between the primary drive pulley72 and the driveshaft 12. A sprag clutch employs sprags (not shown),that due to their oblong shape, wedge between driveshaft 12 and theouter sprag bearing race 78, when rotation occurs in a first direction,but allow driveshaft 12 and outer sprag race 78 to move independently ofeach other when rotation occurs in the opposite direction. Furthermore,upon rapid deceleration of the primary drive pulley 72 rotational speed,the sprag clutch 71 disengages and allows driveshaft 12, drive gear 30,impeller shaft 20, and impeller 22 to overrun and gently coast to areduced rotational speed. As shown in FIG. 4D, the feature of thepresent invention dramatically reduces the peak destabilizing event, orrapid deceleration. The wedging action of the sprags locks driveshaft 12and the outer sprag bearing races 78 together, thereby enabling thetransfer of rotational force, or torque between the engine 14 and thedriveshaft 12.

By way of example, a FORMSPRAG® sprag clutch (part number CL42875) canbe used as the clutch in the present invention (FORMSPRAG is aregistered trademark of Dana Corporation of Toledo, Ohio). Of course,other types of clutches, including, but not limited to roller clutches,spring clutches, centrifugal clutches, friction clutches, non-frictionclutches, mechanical clutches, pneumatic clutches, hydraulic clutches,electrical clutches, diaphragm clutches and hysteresis clutches, can beemployed without departing from the scope of the present invention. Itwill be appreciated that the disengagement device 70 may be locatedanywhere between the engine 14 and the impeller 22. For example, thedisengagement device 70 may be located between the driveshaft 12 and theimpeller shaft 20, or between the impeller shaft 20 and the impeller 22.

According to other embodiments, the disengagement device 70 may comprisea speed-sensitive engagement mechanism such as a traditional centrifugalclutch. Alternatively, the disengagement device 70 may comprise both aspeed-sensitive engagement feature and an overrunning or disengagingfeature. Advantageously, the speed-sensitive engagement feature permitsthe supercharger 10 to be substantially disengaged from the engine 14during very low speed operation and engine idle, when supercharger 10noise maybe objectionable.

High-performance superchargers (such as for competitive drag racingapplications) require high rotational speeds that create high air-flowand pressure ratios, thereby creating significant rotordynamic problemsand challenges. One such problem is the inherent lack of stiffness atthe impeller-to-impeller shaft shoulder connection point. In a typicalsupercharger, the impeller abuts against a spacer, which in turn abutsagainst a shoulder on the impeller shaft. The diameter of the impellershaft shoulder is normally only slightly larger than the diameter of theimpeller shaft, thereby resulting in a relatively low bending stiffnessin the region between the impeller and the adjacent support bearing. Lowstiffness in this region may result in impeller shaft bending atrotational speeds that are within the range of the supercharger'shigh-speed operation, giving rise to rotordynamic critical speeds,identified by dynamic instabilities and/or excessive vibration.Excessive impeller shaft bending and associated dynamic instabilitiesfrequently results in the impeller contacting the compressor housing,causing catastrophic failure of the impeller.

Referring to FIGS. 5A and 5B, another feature of the present inventionis illustrated. A spacer assembly 80 is disposed around the impellershaft 20 between the impeller 22 and the impeller shaft inner bearingrace 81. The impeller shaft 20 comprises a distal section 20 a, which isadjacent to the impeller 22, and has a first diameter. A proximalsection 20 b is adjacent to the impeller shaft inner bearing race 81,and has a second, larger diameter. The first and second impeller shaftsections 20 a, 20 b meet at a transition section 20 c. The spacerassembly 80 comprises a tubular spacer 84 disposed between the impeller22 and the transition section 20 c and an impeller spacer 82 disposedbetween the tubular spacer 84 and the base of the impeller 22. The twospacers 82, 84 mechanically couple the distal impeller shaft section 20a to the impeller shaft inner bearing race 81, resulting in a muchstiffer construction and a significant reduction in vibration betweencomponents. Put differently, the tubular spacer 84 adds additionalsupport to the distal impeller shaft section 20 a by contacting, andsupporting the impeller spacer 82 at a diameter that is approximate tothe diameter of the impeller shaft inner bearing race 81.

As best seen in FIG. 5A, transition section 20 c preferably comprises acurvilinear taper providing a gradual transition between the first andsecond impeller shaft sections. In the illustrated embodiment,transition section 20 c is substantially concave. However, as would beunderstood to those of ordinary skill in the art, transition section 20c may also be substantially convex or substantially straight, withoutdeparting from the scope of the present invention. Advantageously, thetransition section 20 c is configured to significantly reduce impellershaft stress at critical rotational speeds. More particularly, thetubular spacer 84 allows the transition section 20 c to be shaped in apreferred configuration, e.g., a fillet with generous radius, therebydramatically increasing the fatigue resistance of the impeller shaft 20.This is because the transition section 20 c can be shaped to minimizelocalized stresses, thereby eliminating or minimizing the formation offatigue cracks.

Referring now to FIG. 5B, other advantages of replaceable shaft-bearingcartridge 68 become apparent. In this preferred embodiment, bearings 40a, 40 b are of the angular contact type, and are mounted as duplextandem pairs, known in the art as “DT”, with the pairs, in turn mounted“back-to-back” to each other. Bearings 40 a are firmly retained toimpeller shaft 20 proximal section 20 b by retaining washer 86 andthreaded fastener 87, which engages a mating threaded receptacle inproximal section 20 b. Bearings 40 b are retained by spacers 84, 82,impeller 22, washer 88 and impeller fastener 89, which engages a matingthreaded portion of distal section 20 a. Preferably, a static preloadforce should be applied in order to maintain stability of 40 a, 40 b.Preload is provided by spring elements 83, which generate a preloadforce against retainers 85. In this preferred embodiment, the preloadforce may range from about 50 lbf to about 400 lbf.

Alternative embodiments are also possible, and these are described andincorporated herein as within the scope of the present invention. In onesuch embodiment, angular contact bearings 40 a, 40 b may be configuredas rigidly preloaded duplex sets, and mounted either back-to-back (knownin the art as “DB”) or face-to-face (known in the art as “DF”).Advantageously, the clamping forces acting on bearings 40 a, 40 b innerraces are developed by threaded fastener 87 and impeller fastener 89,which in turn enable the rigid preloading of bearings 40 a, 40 b.

Referring now to FIGS. 6A and 6B, high performance superchargers oftenhave air, or gas flow rates that exceed 200 lbm/min. and pressure ratiosexceeding 3.0 (i.e., pressures greater than three times ambientatmospheric pressure). Of course, this places extraordinary demands onmost centrifugal superchargers and their associated impellers. Properimpeller design is critical for the overall performance of thesupercharger. A primary impeller design challenge involves attainingsufficient airflow performance without resorting to undesirable designs.An example of an undesirable design is an impeller having excessivelylarge passageways, which preclude aerodynamic choke, but result in poorblade loading and other deleterious effects.

On one hand, it is desirable to have a low blade count at the impellerinlet to decrease aerodynamic blockage and increase airflow. On theother hand, in order to increase impeller efficiency, a high blade countis preferred further along the airflow passageway (especially near theimpeller outlet). Such a design allows the specific impeller work (e.g.,total work per unit blade) to be reduced, thereby reducing blade loadingeffects to more efficient levels.

Referring to FIGS. 6A and 6B, another feature of the present inventionis illustrated. An impeller 22 suitable for use with the supercharger 10is shown. Impeller 22 preferably comprises at least three sets of bladesincluding primary blades 22 a, secondary blades 22 b, and tertiaryblades 22 c. In the illustrated embodiment, the impeller 22 comprises aset of primary blades 22 a having a first height, a set of secondaryblades 22 b having a second height, and a set of tertiary blades 22 chaving a third height. The blade heights are configured such that thefirst height is greater than the second height, which is greater thanthe third height. As would be understood to those of ordinary skill inthe art, the impeller 22 may consist of additional or fewer sets ofblades having different heights without departing from the scope of thepresent invention.

As depicted in FIG. 2A, air or other gasses are drawn into the impellerthrough opening 24 a in the compressor housing 24. Referring to FIG. 6B,the air enters the impeller 22 through the inlet region 90, which has arelatively low blade count since the secondary blades 22 b and tertiaryblades 22 c do not extend up to the top of the impeller 22. The air iscompressed as it travels through a middle region 92 having a relativelymedium blade count and a lower region 94 having a relatively high bladecount since all three sets of blades extend through this region.

Specifically, in a preferred embodiment (as shown in FIGS. 6A and 6B) ofthe present invention, the impeller 22 would include five primary blades22 a, five secondary blades 22 b, and 10 tertiary blades 22 c.Alternative embodiment impellers 22 may have a range of 3 to 9 primaryblades 22 a, with 3 to 9 secondary blades 22 b, and 6 to 18 tertiaryblades 22 c. It will be appreciated that other blade numbers and/orarrangements may be employed without departing from the scope of thepresent invention.

One feature of this aspect of the invention is that the relatively lowblade count within inlet region 90 induces a low density air flow thatminimizes aerodynamic blockage. Conversely, the relatively high bladecount within outlet region 96 provides excellent aerodynamic performanceby minimizing blade loading.

Referring now to FIGS. 7A and 7B; centrifugal compressors forsuperchargers commonly employ an exit assembly such as a compressorhousing or volute. Compressor housings are often complex structures thatpose both design and manufacturing difficulties. By way of example, onemanufacturing problem involves providing access to the inner flow pathpassage for cleaning (e.g., polishing) and/or maintenance. Othermanufacturing problems relate to installing and supporting the core inthe mold when casting the compressor housing. Complex cores result inunacceptably high reject rates, but simpler cores limit design optionsin the critical diffuser region.

As shown in FIGS. 7A and 7B, another feature of the present invention isillustrated. A modular compressor housing 24 suitable for use with thesupercharger 10 is depicted. The modular compressor housing 24 comprisesat least two modular components as opposed to a single casting. In theillustrated embodiment, modular compressor housing 24 comprises threemodular components including a main housing or scroll 98, a shroud 100and a backplate 102. As an assembly, shroud 100 and backplate 102 forman annular space or diffuser passageway 104. Alternatively, two of thethree components can be combined into a single component, therebyforming a, modular compressor housing 24 having two components. Forexample, the shroud 100 and scroll 98 may be combined into a singlecomponent.

As shown in a preferred embodiment of FIG. 7A, diffuser passageway 104is curved approximately 45° toward the axial direction, resulting in amore compact overall dimension of compressor housing 24. Advantageously,curved diffuser passageway 104 affords a reduction in compressor housing24 dimension without unduly shortening the length of diffuser passageway104. Shortening the length of the diffuser passageway reduces themaximum pressure recovery attainable from the diffuser, whichdeleteriously affects performance of the compressor stage. The amount ofcurvature toward the axial may range from 20° to 60° without departingfrom the scope of this feature of the invention.

Referring to FIG. 7B, shroud 100 may be cast and machined separately andattached to the main housing 98 using fasteners such as screws, bolts,or other suitable fasteners. The backplate 102 may be attached to themain housing 98 by way of force-fit or friction fit, thereby coveringthe shroud 100. Alternatively, the backplate 102 may be attached usingsuitable removable fasteners. Advantageously, by removing the backplate102 and shroud 100 components, the interior of the compressor housing 24is accessible for blending, de-burring, polishing, cleaning, and/ormaintenance. Additionally, the compressor housing 24 may incorporatealternative diffusers including, but not limited to, vaneless diffusers,channel or wedge diffusers and low-solidity vane diffusers.Advantageously, the modular design of the compressor housing 24 permitsdifferent diffusers to be installed, thereby enabling compressor“tuning.” This reduces the number of parts that must be maintained instock, thus reducing costs. Also advantageously, the modular designaffords ease of manufacture of the curved diffuser passageway 104.

Thus, it is seen that a centrifugal supercharger is provided. Oneskilled in the art will appreciate that the present invention can bepracticed by other than the above-described embodiments, which arepresented in this description for purposes of illustration and not oflimitation. The description and examples set forth in this specificationand associated drawings only set forth preferred embodiment(s) of thepresent invention. The specification and drawings are not intended tolimit the exclusionary scope of this patent document. Many designs otherthan the above-described embodiments will fall within the literal and/orlegal scope of the following claims, and the present invention islimited only by the claims that follow. It is noted that variousequivalents for the particular embodiments discussed in this descriptionmay practice the invention as well.

1. A supercharger, comprising: a rotatable shaft; at least one bearingassembly disposed around a portion of the rotatable shaft, said bearingassembly being constructed of a first material having a predeterminedcoefficient of thermal expansion; a housing surrounding the bearingassembly, said housing being constructed of a second material having acoefficient of thermal expansion different from said coefficient ofthermal expansion of said first material; and an intermediate memberformed of a ferrous-based material and disposed in a stationarydisposition between the bearing assembly and the housing, separate fromand adjacent to said bearing assembly and proximate said housing, saidintermediate member being constructed of a material having a coefficientof thermal expansion substantially similar to the coefficient of thermalexpansion of said first material whereby alignment of said bearingassembly with respect to the rotating shaft is maintained during highspeed operation of the supercharger.
 2. The supercharger of claim 1,wherein the ferrous-based material is selected from a group consistingof: a gray iron, a G2-grade gray iron, a DURA-BAR, a free machiningsteel, a 12L14 steel, a 1018 steel, a ferrous based iron, a steel, and asteel alloy.
 3. The supercharger of claim 1, wherein the material ofwhich said intermediate member is constructed has a coefficient ofthermal expansion that may range between about 0.000004 and 0.000007in/in-° F.
 4. The supercharger of claim 1, wherein the intermediatemember is selected from a group consisting of: a sleeve, and a sheath.5. The supercharger of claim 1, wherein the housing element is comprisedof aluminum.
 6. The supercharger of claim 1, wherein the rotatableshaft, bearing assembly, and intermediate member comprise a thermallystable replaceable cartridge assembly.
 7. A supercharger having animpeller shaft defining a proximal section, a distal section of areduced diameter and a transitional section disposed therebetween, animpeller directly mounted on the distal section of the impeller shaftand at least one bearing assembly positioned about a portion of theproximal section of the impeller shaft, the improvement comprising aspacer assembly positioned circumferentially on the impeller shaftbetween the impeller and the bearing assembly, said spacer assemblycomprising a first tubular spacer and a second spacer, said firsttubular spacer being positioned about a second portion of said proximalsection of the impeller shaft and said transitional section thereof andbearing against said bearing assembly and said second spacer, saidsecond spacer being separable from said first tubular spacer andpositioned adjacent to and bearing against a base of the impellerwhereby said spacer assembly provides stiffening support for saidimpeller shaft proximate said transitional section thereof.
 8. Thesupercharger of claim 7, wherein said spacer assembly is structured tocouple said impeller to said bearing assembly.
 9. The supercharger ofclaim 7, wherein the axial length of said first tubular spacer issubstantially greater than the axial length of said second spacer. 10.The supercharger of claim 7, wherein the axial length of said firsttubular spacer is substantially greater than the axial length of saidsecond spacer and wherein the radial length of the portion of saidsecond spacer bearing against said impeller is substantially greaterthan the radial length of said first tubular spacer bearing against saidbearing assembly.